Semiconductor light emitting device and fabrication method thereof

ABSTRACT

Semiconductor light emitting devices and methods of producing same are provided. The semiconductor light emitting devices include a substrate that has a surface including a difference-in-height portion composed of, for example, a wurtzite compound. A crystal growth layer is formed in the substrate surface wherein at least a portion of which is oriented along an inclined plane with respect to a principal plane of the substrate. The semiconductor device includes a first conductive layer, an active layer and a second conductive layer formed on the crystal layer in a stacked arrangement and oriented along the inclined place.

RELATED APPLICATION DATA

[0001] The present application claims priority to Japanese PatentDocument No. P2000-381249 filed on Dec. 15, 2000 herein incorporated byreference to the extent permitted by law.

BACKGROUND OF THE INVENTION

[0002] The present invention generally relates to semiconductor devices.More specifically, the present invention relates to semiconductorlight-emitting devices and processes for producing same.

[0003] It is known that semiconductor light emitting devices can befabricated by forming a low temperature buffer layer overall on asapphire substrate, forming an n-side contact layer made from GaN dopedwith Si thereon, and stacking an n-side cladding layer made from GaNdoped with Si, an active layer made from InGaN doped with Si, a p-sidecladding layer made from AlGaN doped with Mg, and a p-side contact layermade from GaN doped with Mg thereon. As commercial products ofsemiconductor light emitting devices having such a structure, lightemitting diodes and semiconductor lasers for emitting light of blue andgreen having a wavelength of 450 nm to 530 nm have been fabricated on alarge scale.

[0004] With respect to growing gallium nitride (GaN), a sapphiresubstrate has been often used; however, in this case, dislocations maybe contained in the grown crystal at a high density because ofmismatching in lattice between the sapphire substrate and the galliumnitride to be grown thereon. From this viewpoint, a technique forforming a low temperature buffer layer on a substrate is effective tosuppress defects caused in the crystal to be grown on the substrate.Further, a method of reducing crystal defects by usual epitaxial growthin combination with epitaxial lateral overgrowth (ELO) has beendisclosed in Japanese Patent Laid-open No. Hei 10-312971.

[0005] Japanese Patent Laid-open No. Hei 10-312971 regarding a method offabricating a semiconductor light emitting device describes thatthrough-dislocations propagated in the direction perpendicular to asubstrate principal plane is deflected in the lateral direction by afacet structure formed in a growth region during fabrication of thedevice, so that it is possible to block the propagation of thethrough-dislocation and hence to reduce crystal defects.

[0006] A light emitting system including a plurality of semiconductorlight emitting devices in the form of light emitting diodes orsemiconductor lasers is usable for an image display unit by using, aseach of pixels arrayed in a matrix, a combination of light emittingdiodes or semiconductor lasers of blue, green, and red, andindependently driving the pixels; and is also usable for a white lightemitting unit or an illumination unit by making the light emittingdevices of blue, green, and red simultaneously emit light of blue,green, and red. In particular, since a light emitting device using anitride semiconductor has a band gap energy ranging from about 1.9 eV toabout 6.2 eV, it can realize a full-color display only by using onematerial. For this reason, a multi-color light emitting device using anitride semiconductor has been actively studied. It is to be noted thatthe term “nitride” used herein means a compound which contains one ormore of B, Al, Ga, In, and Ta as group III elements and N as a group Velement, and which may contain impurities in an amount of 1% or less ofthe total amount or 1×10²⁰ cm³ or less.

[0007] A technique of forming a multi-color light emitting device on thesame substrate has been known, wherein a plurality of regions foremitting light of respective colors, which include active layers havingdifferent band gap energies corresponding to different emissionwavelengths, are stacked, and a common electrode on the substrate sideis provided while electrodes on the other side are individually providedon the light emission regions. In another known multi-color lightemitting device, the regions for emitting light of respective colors arestepwise formed on the substrate for easy extraction of electrodestherefrom. The multi-color light emitting device of this type in which aplurality of layers including a pn-junction are stacked has apossibility that the light emission regions in the same device act justas a thyristor, and to prevent such operation similar to that of athyristor, a multi-color light emitting device, in which grooves areformed between one and another of the stepwise light emission regionsfor isolating the light emission regions from each other, has beendisclosed, for example, in Japanese Patent Laid-open No. Hei 9-162444.

[0008] Further, a light emitting device disclosed in Japanese PatentLaid-open No. Hei 9-92881 is configured such that, to realizemulti-color light emission, an InGaN layer is formed on an aluminasubstrate via an AlN buffer layer, wherein a portion of the InGaN layeris doped with Al to form a blue light emission region, another portionof the InGaN layer is doped with P to form a red light emission region,and a non-doped portion of the InGaN layer is taken as a green lightemission region.

[0009] The above-described techniques, however, have the followingproblems. Known epitaxial lateral overgrowth techniques and knowncrystal growth methods characterized by forming a facet structure in agrowth region are advantageous in that since the propagation ofthrough-dislocations can be deflected by a facet structure portion orthe like, crystal defects can be significantly reduced. However, to forma light emission region including an active layer after epitaxiallateral overgrowth or formation of the facet structure, the epitaxiallateral overgrowth is further performed or the facet structure is buriedso as to obtain a flat plane on which the light emission region is to beformed, with a result that the number of processing steps is increasedand a time required for fabricating the device is prolonged.

[0010] Known multi-color light emitting devices are disadvantageous inthat since the processing steps become complicated, it fails to form thelight emitting device at a high accuracy, and since the crystallinity isdegraded, it fails to provide good light emission characteristic. Forthe multi-color light emitting device in which grooves are formedbetween one and another of the stepwise light emission regions forisolating the light emission regions from each other, anisotropicetching must be repeated by several times for isolating the lightemission regions including active layers from each other. This causesproblems that since the crystallinity of each of the substrate and thesemiconductor layer may be degraded by dry etching, it is difficult tosustain desirable crystallinity, and that since etching is repeated byseveral times, the number of steps required for mask alignment andetching is increased.

[0011] For the multi-color light emitting device in which impurities areselectively doped in the single active layer formed on the substrate,since a margin must be provided for forming an opening portion in themask layer, a sufficient distance must be set between one and another ofthe different light emission regions, particularly, in the case ofpreviously estimating a fabrication error, so that it is difficult toform a micro-side light emitting device, and further, the number ofsteps is increased by selective doping.

SUMMARY OF THE DETENTION

[0012] An advantage of the present invention is to provide asemiconductor light emitting device capable of reducing occurrence ofcrystal defects such as through dislocations without increasing thenumber of fabrication steps and to provide a method of fabricating thesemiconductor light emitting device.

[0013] Another advantage of the present invention is to provide asemiconductor light emitting device including light emission regionshaving different emission wavelengths, which is allowed to be fabricatedat a high accuracy with a reduced number of steps and which is excellentin crystallinity, and to provide a method of fabricating thesemiconductor light emitting device.

[0014] In an embodiment of the present invention, there is provided asemiconductor light emitting device including: a first conductivecladding layer, an active layer, and a second cladding layer; wherein adifference-in-height portion is formed in a surface of a wurtzite-typecompound semiconductor layer; a crystal growth layer having an inclinedplane is formed by crystal growth on the surface, having thedifference-in-height portion, of the compound semiconductor layer; andthe first conductive cladding layer, the active layer, and the secondconductive layer are sequentially formed on the crystal growth layer insuch a manner as to be approximately in parallel to the inclined planeof the crystal growth layer.

[0015] In an embodiment of the present invention, there is provided amethod of fabricating a semiconductor light emitting device, includingthe steps of: forming a wurtzite-type compound semiconductor layer on asubstrate principal plane in such a manner that a difference-in-heightportion is formed in a surface of the compound semiconductor; forming acrystal growth layer having an inclined plane inclined with respect tothe substrate principal plane by crystal growth on the surface, havingthe difference-in-height portion, of the compound semiconductor layer;and stacking a first conductive cladding layer, an active layer, and asecond conductive layer in a region extending in parallel to theinclined plane.

[0016] With these configurations of the semiconductor light emittingdevice and the method of fabricating the semiconductor light emittingdevice according to the present invention, since a wurtzite typecompound semiconductor layer having a difference-in-height portion isformed on a substrate principal plane, a crystal growth layer having afacet structure can be formed by making use of a difference in crystalgrowth rate between crystal growth directions at thedifference-in-height portion. Since such a facet structure has aninclined plane inclined with respect to the substrate principal plane,it is possible to sufficiently reduce occurrence of crystal defects suchas through-dislocations at the inclined plane. The stacked structure ofa first conductive cladding layer, an active layer, and a secondconductive cladding layer functions as a light emission region byinjecting a current thereto. In particular, according to the presentinvention, since the inclined plane inclined with respect to thesubstrate principal plane is utilized while being left as not buried, itis possible to reduce occurrence of dislocations, and to facilitate thefabrication process because of elimination of the need of burying theinclined plane.

[0017] To achieve the second object, according to a third aspect of thepresent invention, there is provided a semiconductor light emittingdevice including: a first conductive cladding layer, an active layer,and a second active cladding layer; wherein a wurtzite-type compoundsemiconductor layer is formed on a substrate principal plane in such amanner that a difference-in-height portion is formed in a surface of thecompound semiconductor; a crystal growth layer having an inclined planeinclined with respect to the substrate principal plane is formed bycrystal growth on the surface, having the difference-in-height portion,of the compound semiconductor layer; the first conductive claddinglayer, the active layer, and the second conductive layer aresequentially formed on two or more crystal planes including the inclinedplane of the crystal growth layer, to form light emission regions; andelectrodes are independently formed in the light emission regions formedon the two or more crystal planes.

[0018] With this configuration of the semiconductor light emittingdevice according to the present invention, a first conductive claddinglayer, an active layer, and a second conductive layer are sequentiallyformed on two or more crystal planes including an inclined plane of acrystal growth layer, to form light emission regions; and electrodes areindependently formed in the light emission regions formed on the two ormore crystal planes. Since the independent electrodes are formed, thelight emission regions are independently operated by supplying separatesignals to the independent electrodes. As a result, light can beindependently emitted from the two light emission regions of one device,and since light having different wavelengths can be emitted from thelight emission regions of one device, the device can be used as amulti-color light emitting device.

[0019] Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the Figures.

BRIEF DESCRIPTION OF THE FIGURES

[0020]FIGS. 1A to 1G are sectional views showing steps of fabricating asemiconductor light emitting device according to an embodiment of thepresent invention. FIG. 1A illustrates the step of forming a GaN layerdoped with Si. FIG. 1B shows the step of forming a mask layer. FIG. 1Cshows the step of forming difference-in-height portions. FIG. 1D showsthe step of forming facet structures each having inclined planes. FIG.1E shows the step of forming a GaN layer doped with Mg. FIG. 1F showsthe step of forming an n-side electrode. FIG. 1G shows the step offorming a p-side electrode.

[0021]FIGS. 2A to 2G are sectional views showing steps of fabricating asemiconductor light emitting device according to an embodiment of thepresent invention. FIG. 2A shows the step of forming a GaN layer dopedwith Si. FIG. 2B shows the step of forming a mask layer. FIG. 2C showsthe step of forming difference-in-height portions. FIG. 2D shows thestep of forming facet structures each having inclined planes. FIG. 2Eshows the step of forming a GaN layer doped with Mg. FIG. 2F shows thestep of forming an n-side electrode. FIG. 2G shows the step of forming ap-side electrode.

[0022]FIG. 3 is a perspective view showing a step of fabricating asemiconductor light emitting device according to an embodiment of thepresent invention, wherein a facet structure is shown in a developmentstate that has a honeycomb-type inverse-hexagonal shape.

[0023]FIGS. 4A and 4B are views showing portions of the semiconductorlight emitting device according to an embodiment of the presentinvention. FIG. 4A shows a planar shape of a difference-in-heightportion. FIG. 4B shows a cross-sectional shape of a facet.

[0024]FIGS. 5A to 5F are sectional views showing steps of fabricating asemiconductor light emitting device according to an embodiment of thepresent invention. FIG. 5A shows the step of forming a silicon oxidelayer. FIG. 5B shows the step of forming an opening portion in a resistlayer. FIG. 5C shows the step of forming a window portion in the siliconoxide layer. FIG. 5D shows the step of forming an electrode by alift-off process. FIG. 5E shows the step of removing the resist layer.FIG. 5F shows the step of forming an n-side electrode.

[0025]FIGS. 6A to 6D are sectional views showing steps of fabricating asemiconductor light emitting device according to an embodiment of thepresent invention. FIG. 6A shows the step of forming a silicon oxidelayer. FIG. 6B shows the step of forming an opening portion in a resistlayer. FIG. 6C shows the step of forming an electrode by a lift-offprocess. FIG. 6D shows the step of forming an n-side electrode.

[0026]FIG. 7 is a sectional perspective view showing a semiconductorlight emitting device according to an embodiment of the presentinvention.

[0027]FIG. 8 is a sectional perspective view showing a semiconductorlight emitting device according to an embodiment of the presentinvention.

[0028]FIG. 9 is a sectional perspective view showing an example of alight emission state of the semiconductor light emitting deviceaccording to an embodiment of the present invention.

[0029]FIG. 10 is a sectional perspective view showing a semiconductorlight emitting device according to an embodiment of the presentinvention.

[0030]FIG. 11 is a sectional perspective view showing a semiconductorlight emitting device according to an embodiment of the presentinvention.

[0031]FIG. 12 is a sectional view showing a semiconductor light emittingdevice according to an embodiment of the present invention, wherein thedevice is connected to a current quantity adjusting circuit.

DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention relates to semiconductor devices. Inparticular, the present invention relates to semiconductor lightemitting devices and methods of producing same.

[0033] In an embodiment, a semiconductor light emitting device includesa wurtzite-type compound semiconductor layer having in its surface adifference-in-height portion is formed on a principal plane of asubstrate; a crystal growth layer including a facet structure having aninclined plane inclined with respect to the principal plane of thesubstrate wherein the crystal growth layer is formed by crystal growthon the surface, having the difference-in-height portion, of the compoundsemiconductor layer; and a first conductive cladding layer, an activelayer, and a second conductive cladding layer are formed in a regionextending in parallel to the inclined plane.

[0034] It should be appreciated that any suitable type of material ormaterials can be utilized to fabricate the semiconductor light emittingdevice of the present invention to the extent that a wurtzite-typecompound semiconductor layer can be formed on the substrate. Forexample, the substrate may be made from a sapphire (Al203, whosedesirable crystal plane is an A-plane, R-plane, or C-plane), SiC (havinga structure of 6H, 4H or 3C), GaN, Si, ZnS, ZnO, AIN, LiMgO, LiGaO2,GaAs, MgAl₂O₄, InAlGaN-like or combination thereof. The substrate can beformed into any suitable shape or configuration. In an embodiment, thesubstitute material includes a hexagonal system, cubic system or thelike, preferably a hexagonal system. For example, in the case of growinga gallium nitride (GaN) based compound semiconductor on a substrate, itmay be desirable that the substrate be made from sapphire with itsC-plane taken as a principal plane of the substrate. It is to be notedthat the crystal plane of sapphire used for the substrate principalplane is not strictly limited to the C-plane but may be substantiallyequivalent to the C-plane. For example, the substrate principal planemay be positioned relative to the C-plane at an angle ranging from about5° to about 6°.

[0035] A compound semiconductor layer to be formed on the substrateprincipal plane may be made from a nitride semiconductor having awurtzite-type crystal structure, a BeMgZnCdS based semiconductor layer,a BeMgZnCdO based compound semiconductor layer or the like because afacet structure will be formed thereon in the subsequent step.

[0036] As the above nitride semiconductor having a wurtzite-type crystalstructure, there may be used a group III based compound semiconductor,for example, a gallium nitride (GaN) based compound semiconductor, analuminum nitride (AlN) based compound semiconductor, an indium nitride(InN) based compound semiconductor, an indium gallium nitride (InGaN)based compound semiconductor aluminum gallium nitride (AlGaN) basedcompound semiconductor or the like. In particular, a gallium nitridebased compound semiconductor is preferably used as the material forforming the nitride semiconductor layer to be formed on the substrate.It is to be noted that a nitride semiconductor such as InGaN, AlGaN, orGaN is not necessarily composed of only a ternary or binary mixedstructure. For example, an InGaN semiconductor may contain an impuritysuch as a trace of Al in a range not changing the function of InGaN. Inthis specification, the term “nitride” means a compound which containsone or more of B, Al, Ga, In, and Ta as the group III elements and N asthe group V element, and which may contain impurities in an amount of 1%of the total amount or less or 1×10²⁰ cm³ or less.

[0037] The compound semiconductor layer may be grown on the substrate byone of various vapor phase growth processes, for example, a metalorganic chemical deposition (MOCVD), metal organic vapor phase epitaxialgrowth (MOVPE) process, a molecular beam epitaxial growth (MBE) process,a hydride vapor phase epitaxial growth (HVPE) process or the like. In anembodiment, the MOVPE process is preferred as it is capable of growingthe compound semiconductor layer with a high crystallinity on thesubstrate at a high processing rate. In the MOVPE process, typically, analkyl metal compound is used as each of Ga, Al and In sources, forexample, TMG (trimethyl gallium), TEG (triethyl gallium), or the like,is used as the Ga source, TMA (trimethyl aluminum), TEA (triethylaluminum), or the like, is used as the Al source, and TMI (trimethylindium), TEI (triethyl indium), or the like, is used as the In source.The MovPE process can also include a gas such as ammonia or hydradine asa nitrogen source; silane gas as an Si (impurity) source, Cp2Mg(cyclopentadienyl magnesium) as a Mg (impurity) source, a DEZ (diethylzinc) gas as a Zn (impurity) source or the like. According to the MOVPEprocess, for example, an InAlGaN based compound semiconductor layer canbe grown on the substrate by supplying gases composed of In, Al, Ga andN sources and/or a gas as an impurity source to the front surface of thesubstrate heated, for example, at 600° C. or more, to decompose thesource gases, thereby allowing epitaxial growth of an InAlGaN basedcompound semiconductor on the substrate.

[0038] In an embodiment, to form a facet structure having an inclinedplane inclined with respect to the substrate principal plane by crystalgrowth, a difference-in-height portion is formed in a surface of theabove-described compound semiconductor layer as an under layer forcrystal growth. The difference-in-height portion functions to make,during crystal growth, a growth rate of a crystal plane perpendicular toa crystal plane appearing on the substrate. For example, the substrateprincipal plane different from a growth rate of a crystal plane parallelto the substrate principal plane, to thereby form a facet structure. Inan embodiment, the difference-in-height portion is formed in the surfaceof the compound semiconductor layer by photolithography and anisotropicetching using a mask layer made from silicon oxide or silicon nitride.The shape of the difference-in-height portion is not particularlylimited insofar as the difference-in-height portion allows formation ofa facet structure having an inclined plane inclined with respect to thesubstrate principal plane. For example, the difference-in-height may beformed into a shape selected from a stripe shape, rectangular shape, around shape, a polygonal shape such as a triangular shape or hexagonalshape, or the like. The shape of the difference-in-height portion meansthe planar shape of the difference-in-height portion. For example,according to an embodiment of the present invention, thedifference-in-height portion having a triangular shape means not onlythe difference-in-height portion projecting into a triangular hole butalso the difference-in-height portion recessed into a triangular shape.A plurality of different-in-height portions may be formed overall orpartially on the surface of a compound semiconductor layer. In addition,different difference-in-height portions may be formed in combination.

[0039] After the difference-in-height portion is formed in the compoundsemiconductor layer, a crystal growth layer including a facet structurehaving an inclined plane is formed thereon by crystal growth inaccordance with the same manner as that for forming the above-describedcompound semiconductor layer, for example, one of various vapor phasegrowth processes, such as the metal organic chemical deposition (MOCVD)or metal organic vapor phase epitaxial growth (MOVPE) process, themolecular beam epitaxial growth (MBE) process, or the hydride vaporphase epitaxial growth (HVPE) process. The crystal growth layer formedon the compound semiconductor layer having the difference-in-heightportion is typically made from the same material as that for forming thecompound semiconductor layer. The material for forming the crystalgrowth layer, however, may be made from another compound semiconductormaterial insofar as it can form a facet structure by crystal growthwhile being dependent on the shape of the difference-in-height portion.

[0040] As previously discussed, the crystal growth layer includes afacet structure having an inclined plane inclined with respect to asubstrate principal plane by crystal growth. In an embodiment, theinclined plane includes an S-plane, a {11-22} plane, the like, or planesbeing substantially equivalent thereto. Here, the plane beingsubstantially equivalent to the S-plane means a plane inclined withrespect to the S-plane at an angle ranging from about 5° to about 6°.For example, if the C-plane is selected as the substrate principalplane, it is possible to form the S-plane and the plane beingsubstantially equivalent thereto. The S-plane is a stable plane whichcan be selectively grown on the C+ plane. The S-plane is expressed by a(1-101) plane in Miller index for the hexagonal system. The C+ plane andC− plane are present as the C-plane, and similarly, the S+ plane and S−plane are present as the S-plane. According to the present invention,unless otherwise specified, the S+ plane, which is grown on the C+ planeof the GaN layer, is taken as the S-plane. In this regard, the S+ planeis more stable than the S− plane. In addition, the C+ plane is expressedby a (0001) plane in Miller index.

[0041] In the case of growing a gallium nitride based compoundsemiconductor for forming the above-described crystal growth layer, thenumber of bonds of gallium to nitride at the S-plane becomes two orthree, which is the largest among crystal planes excluding the C− plane.Here, since the C− plane cannot be formed on the C+ plane, the number ofbonds of gallium to nitride at the S-plane becomes largest among thecrystal planes. For example, in the case of growing a wurtzite-typenitride on a sapphire substrate using the C+ plane as the principalplane, the surface of the nitride generally becomes the C+ plane;however, the S-plane can be stably formed by making use of selectivegrowth. At a plane parallel to the C+ plane, nitrogen liable to beeliminated is bonded to gallium via a single bond. On the other hand, atan inclined S-plane, nitrogen is bonded to gallium via at least one ormore bonds. In this regard, at the S-plane, a V/III ratio is effectivelyincreased, to improve the crystallinity of the crystal growth layer.Further, in the case of forming the crystal growth layer, it is grownalong the direction different from the orientation of the C+ plane ofthe substrate. In this regard, since dislocations propagated upwardlyfrom the substrate are deflected, it is possible to reduce occurrence ofcrystal defects.

[0042] It should be appreciated that the type of an inclined plane of afacet structure formed on the crystal growth layer is controlled, forexample, on the basis of a growth condition at the time of crystalgrowth, and shapes of a difference-in-height portion and a mask portion.For example, in the case where a difference-in-height portion extendingin a stripe shape is formed in a surface of a gallium nitride-basedsemiconductor layer where the longitudinal direction of the stripe is a<11-20> direction, a facet structure having the S-plane as an inclinedplane is formed. In this case, the facet structure is formed into aninverse V-shape in a cross-sectional view taken along a planeperpendicular to the longitudinal direction of the stripe. Since theshape of the difference-in-height portion is not limited to the stripeshape, the cross-section of the crystal growth layer can have any othershape than the stripe shape, for example, a rectangular shape, a roundshape, a triangular shape, a hexagonal shape, or the like. The crystalgrowth layer is grown depending on the shape of the difference-in-heightportion. If the extending direction of an end portion of thedifference-in-height portion is set to be approximately perpendicular toa <1-100> direction or the <11-20> direction, then a difference ingrowth rate between growth in the lateral direction and growth in thevertical direction appears necessarily results in a facet structure. Inan embodiment, crystal growth temperature at the time of growth of thecrystal growth layer is about 1100° C. or less. If the crystal growthtemperature is higher than 1100° C., there occurs an inconvenience thatcharacteristics (particularly, optical characteristic) of the crystal isdegraded. In an embodiment, a pressure at the time of growth of thecrystal growth layer is about 100 Torr or more. If the pressure is lessthan 100 Torr, there occurs an inconvenience that the growth conditionis varied, so that a desired crystal plane cannot be obtained and aconductivity of the crystal growth layer becomes poor.

[0043] In one embodiment, the semiconductor device of the presentinvention includes a first conductive cladding layer, an active layer,and a second conductive cladding layer stacked on the crystal growthlayer having the facet structure in a region extending in parallel tothe inclined plane of the facet structure. In an embodiment, a crystalgrowth temperature at the time of growth of an InGaN active layer is setin a range of about 700° C. to about 800° C. At such a crystal growthtemperature, since a decomposition efficiency of ammonia is low, theamount of an N source must be increased. As a result of observing afacet structure grown on a crystal growth layer by using cathodeluminescence in an experiment performed by the inventors, it wasrevealed that the S-plane taken as an inclined plane of the facetstructure has a desirable crystallinity and exhibits a higher luminousefficiency as compared with the C+ plane. As a result of observation ofthe surface of the inclined plane by AFM, it was found that the surfacewas suitable for incorporation of InGaN.

[0044] It was also found that the growth of the S-plane allows the layerdoped with Mg to be grown in a good surface state and makes a dopingcondition for the layer doped with Mg very different from a dopingcondition for the layer doped with Mg formed on the C+ plane. As aresult of microscopic photoluminescence mapping, although the surface ofthe layer doped with Mg formed on the C+ plane by the usual manner hasan unevenness of a pitch of about 1 μm, the surface of the layer dopedwith Mg formed on the S-plane obtained by selective growth was even andmeasured at a resolution of about 0.5 mm to about 1 μm. Further, as aresult of observation by SEM, it was revealed that the flatness of theinclined plane, that is, the S-plane is superior to that of the C+plane.

[0045] With respect to the first conductive cladding layer, the activelayer, and the second conductive cladding layer, which are layered in astacked arrangement in the region extending in parallel to the inclinedplane, the conductive type of the first conductive cladding layer is ap-type or an n-type, and the conductive type of the second conductivecladding layer is the n-type or the p-type. For example, in the casewhere a crystal growth layer having the S-plane is made from a galliumnitride based compound semiconductor doped with silicon, a galliumnitride based compound layer doped with silicon may be formed as ann-type cladding layer on the compound semiconductor layer having theS-plane, an InGaN layer can be formed as an active layer thereon, and agallium nitride based compound semiconductor layer doped with magnesiumbe formed as a p-type cladding layer thereon, to thus form a doublehetero structure. The active layer may be of a structure in which anInGaN layer is held between AlGaN layers or an AlGaN layer is providedon one side of the InGaN layer. The active layer may be a single bulkactive layer; however, it may be of a quantum well structure such as asingle quantum well (SQW) structure, a double quantum well (DQW)structure, or a multi-quantum well (MQW) structure. In the case ofadopting the quantum well structure, one or more barrier layers are usedfor separating quantum wells from each other.

[0046] The use of the InGaN layer as the active layer is advantageous infacilitating the fabricating process and enhancing an emissioncharacteristic of the device. Another advantage of the use of the InGaNlayer is that the InGaN layer can be easily crystallized on the S-plane,which has the structure from which nitrogen atoms are less eliminated,with a good crystallinity to enhance the emission efficiency. Inaddition, even in a state that a nitride semiconductor is not doped withan impurity, the conductive type of the nitride semiconductor becomesthe n-type because of nitrogen holes generated in crystal; however, ingeneral, an n-type nitride semiconductor having a desirable carrierconcentration is obtained by doping a doner impurity such as Si, Ge, Se,or the like, in crystal. On the other hand, a p-type nitridesemiconductor is obtained by doping an acceptor impurity such as Mg, Zn,C, Be, Ca, Ba, or the like, in crystal. In this case, to obtain a p-typenitride semiconductor having a high carrier concentration, the nitridesemiconductor having been doped with an acceptor impurity may beannealed in an inert gas atmosphere such as nitrogen or argon, oractivated by irradiation of electron beams, microwaves, or light. Suchan active layer is desirable to be obtained by a semiconductor growthlayer formed only one growth. Only one growth means growth by a singlefilm formation treatment or a sequence of film formation treatments, andtherefore, it does not mean repeated formation of a plurality of activelayers.

[0047] As previously discussed, the first conductive cladding layer, theactive layer, and the second conductive cladding layer extend within aplane parallel to an inclined plane. Such formation of the stackedstructure within a plane parallel to an inclined plane can be easilyperformed by continuing crystal growth, after formation of the inclinedplane. The first conductive cladding layer can be made from the samematerial having the same conductive type as that of the crystal layerhaving the S-plane, and accordingly, after the crystal layer having theS-plane is formed, the same material can be continuously grown byadjusting a concentration thereof. Alternatively, there may be adopted astructure that part of the crystal layer having the S-plane functions asthe first conductive cladding layer.

[0048] According to the semiconductor light emitting device of thepresent invention, inventors have discussed that the luminous efficiencycan be enhanced by making use of a good crystallinity of an inclinedplane formed by crystal growth. In particular, when a current isinjected only in the S-plane having a good crystallinity, the luminousefficiency can be made higher because the S-plane has a high In capturecharacteristic and a good crystallinity. In this regard, to fabricate amulti-color light emitting device by using an InGaN layer, it isdesirable that In can be sufficiently captured as crystal, and theluminous efficiency of the device can be enhanced by making use of agood crystallinity of the S-plane. In the case of crystal growth on theC+ plane, gallium has only one bond to nitrogen liable to be eliminated,and accordingly, when crystal growth is performed by using ammonia whosedecomposition efficiency is low, it is impossible to increase aneffective V/III ratio, with a result that it fails to obtain goodcrystal growth. In the case of crystal growth on the S-plane, since thenumber of bonds of gallium to nitrogen at the S-plane is as large as twoor three, the elimination of nitrogen becomes small and thereby theeffective V/III ratio becomes high. In general, the quality of crystalgrown on not only the S-plane but also any plane other than the C+ planebecomes high because the number of bonds of gallium to nitrogen tends tobe increased for growth on any crystal growth plane other than the C+plane. The growth of crystal on the S-plane is also advantageous in thatthe amount of In incorporated in the crystal grown on the S-planebecomes high. The increased amount of In incorporated in crystal grownon the S-plane is effective for fabricating a multicolor light emittingdevice because a band gap energy is determined on the base of the amountof In incorporated in crystal.

[0049] In an embodiment of the semiconductor light emitting device ofthe present invention, two or three light emission regions having two orthree kinds of emission wavelengths can be formed on the same device.These light emission regions are formed on two or more crystal planesincluding an inclined plane of a crystal growth layer. In the case wherethe substrate principal plane is the C-plane and the inclined plane isthe S-plane, one of the light emission regions is formed in a regionparallel to the S-plane, and another light emission region can be formedin a region of a crystal growth plane corresponding to the C-plane. Theemission wavelength of one light emission region can be made differentfrom that of another light emission region by making at least one of acomposition and a thickness of an active layer between the two lightemission regions, that is, making only the composition of the activelayer, only the thickness of the active layer, or both the compositionand the thickness of the active layer different between the two lightemission regions.

[0050] The composition of an active layer can be adjusted by changing amixing ratio of elements of a ternary or binary mixed crystalconstituting the active layer. In the case of using an InGaN layer asthe active layer, a semiconductor light emitting device for emittinglight of a long-wavelength can be obtained by increasing the amount ofIn contained in the active layer. In crystal growth of an InGaN layer ofan embodiment, a migration length of InGaN, particularly with respect toIn, is estimated about 1 μm to about 2 μm at about 700° C. for optimumcrystal growth of the InGaN layer having a relatively large amount ofIn. This is because InGaN precipitated on a mask is grown from aselective growth portion only by about 1 μm to about 2 μm. The migrationlength of In may be thus regarded as about 1 μm to about 2 μm. Since themigration length of In contained in InGaN in a region from the maskportion of the growth portion is relatively short, that is, about 1 μmto about 2 μm, the content of In or the thickness of InGaN may differ insuch a region.

[0051] The wavelength of light emerged from an active layer is liable tobe changed depending on from which location of the active layer thelight is emerged. This is because the migration length of In is shortenat about 700° C. optimum for crystal growth of the InGaN layer having arelatively large amount of In. According to the semiconductor lightemitting device of the present invention, by making effective use of thefact that the emission wavelength differs between one and another ofregions within the same active layer, first and second light emissionregions having different emission wavelengths are formed in the sameactive layer, and currents are injected in the first and second lightemission regions, respectively. Independent electrodes are formed in thefirst and second light emission regions for independently injectingcurrents therein. In this case, the electrodes on one side (p-side orn-side) in the first and second light emission regions can be utilized.According to an embodiment of the present invention, a multi-colorsemiconductor light emitting device can be obtained by forming two ormore light emission regions having different emission wavelengths in thesame active layer, and independently injecting current therein, andfurther, a semiconductor light emitting device for emitting light of amixed color or white light can be obtained by forming two or more lightemission regions having different emission wavelengths in the sameactive layer, and controlling the device such that the light emissionregions simultaneously emit light.

[0052] In a crystal layer formed on a facet structure having an inclinedplane, an effective V/III ratio is determined by a complicatedcombination of a location, orientation of a crystal plane, and the like.The growth of the facet is also dependent on growth conditions such as agrowth temperature. From experimental data obtained by examining cathodeluminescence of a double hetero structure produced by selective growthin accordance with an embodiment of the present invention, it wasrevealed that the emission wavelength of an upper portion of the doublehetero structure is longer than that of a lower portion of the doublehetero structure by about 100 (nanometers) nm. These experimental datashowed that, by providing different electrodes at different locations ofthe double hetero structure, two or more light emission regions havingdifferent emission wavelengths can be provided with respect to a singlecrystal growth, and therefore, a semiconductor light emitting device foremitting light of multi-colors or emitting white light can be fabricatedvia a single crystal growth.

[0053] For example, in the case of forming a stripe shapeddifference-in-height portion and forming a facet structure having aninclined plane composed of the S-plane obtained by crystal growth andthe C-plane, a light emission region formed on the inclined plane istaken as a long-wavelength light emission region and a light emissionregion formed on the C-plane is taken as a short-wavelength lightemission region. This may be reversed depending on the crystal growthconditions. Also, since the incorporated amount of In differs dependingon a distance from a substrate, an emission wavelength in a higher lightemission region parallel to the C-plane becomes different from anemission wavelength in a lower light emission region parallel to theC-plane. As a result, it is possible to provide a first light emissionregion on the S-plane, a second light emission region on a higher planeparallel to the C-plane, and a third light emission region on a lowerplane parallel to the C-plane.

[0054] Electrodes for independently injecting currents in such lightemission regions having different emission wavelengths are individuallyformed in these light emission regions. In this case, the electrodes onone side (p-side or n-side) can be utilized. To lower a contactresistance, a contact layer may be formed, and then an electrode beformed thereon. In general, each electrode is obtained by forming amulti-layer metal film by vapor-deposition. Such a multi-layer metalfilm may be finely divided into electrodes for respective light emissionregions by photolithography and lift-off, or the like. Each electrodemay be formed on a selective crystal growth layer or one surface of asubstrate; however, to realize electrode wiring at a high density,electrodes may be provided on both the sides. Electrodes provided indifferent regions and independently driven may be formed from the sameelectrode material by photolithography and lift-off, or the like;however, they may be made from different and suitable electrodematerials. A thickness of a resist layer used for lift-off is preferablyin a range of about 1 μm or more. If the thickness of the resist layeris less than about 1 μm, it is difficult to smoothly perform thelift-off and hence to effectively remove the useless metal film.

[0055] Currents may be independently injected in respective lightemission regions having different emission wavelengths. In anembodiment, the semiconductor light emitting device of the presentinvention, which can include a structure including a plurality ofemission regions for emitting light of RGB (red (R), green (G), blue(B)) or CYM (cyan (C), yellow(Y), magenta (M)), is applicable for acolor image display such as a full color display. Further, thesemiconductor light emitting device of the present invention inaccordance with an embodiment which has a structure including aplurality of light emission regions for emitting light of three primarycolors or two or more colors, is applicable for an illuminating unit, orthe like, for emitting light of a mixed color or white light byinjecting the same current in the plurality of light emission regions.

[0056] By way of example, and not limitation, the following examplesillustrate a variety of semiconductor light emitting devices inaccordance with an embodiment of the present invention.

Example One

[0057] A semiconductor light emitting device is fabricated by forming aplurality of stripe shaped difference-in-height portions on a sapphiresubstrate, and forming a crystal growth layer having facet structureseach having inclined planes by making use of the stripe shapeddifference-in-height portions. A method of fabricating the semiconductorlight emitting device and a device structure thereof according to anembodiment will be described with reference to FIGS. 1A to 1G.

[0058] As shown in FIG. 1A, a GaN layer 11 doped with silicon is formedat about 1000° C. on a principal plane (C+ plane) of a sapphiresubstrate 10. In addition, a low temperature buffer layer (not shown)made from AlN or GaN is often formed at a low temperature of about 500°C. between the sapphire substrate 10 and the GaN layer 11. It should beappreciated that the layers of the semiconductor device of the presentinvention can be grown under any suitable operating conditions, such aspressures varying from about 200 Torr or more, including about 740 Torror at about standard or normal pressures.

[0059] As shown in FIG. 1B, a mask layer 12 made from SiO2 or SiN isformed overall on the GaN layer 111 doped with silicon to a thickness ofabout 100 nm to about 500 nm. The mask layer 12 is patterned, byphotolithography and etching using a photoresist layer, into a patternhaving stripe shaped opening portions 13 spaced parallel from each otherwith a specific pitch. The depth of each opening portion 13 is set suchthat the opening portion 13 reaches the GaN layer 11. For example, eachstripe shaped opening portion 13 extends in the <11-20> or <1-100>direction, and a width of the opening portion 13 is in a range of about0.1 μm to about 10 μm. After the opening portions 13 are formed in themask layer 12, the resist layer is removed. In this state, the GaN layer11 is exposed within the opening portions 13 formed in the mask layer12.

[0060] A surface of the GaN layer 11 is selectively etched by using themask layer 12 as a mask, so that the surface of the GaN layer 11 isselectively cut off in a pattern depending on the pattern of the stripeshaped opening portions 13, to form stripe shaped difference-in-heightportions 14. The difference-in-height portion 14 has a high-levelportion which is located directly under a mask portion of the mask layer12 and is thereby not etched, and a low-level portion which is locatedunder the opening portion 13 and is thereby etched. In a plan view, thestripe pattern of the difference-in-height portions 14 corresponds tothe stripe pattern of the opening portions 13 of the mask layer 12.After the difference-in-height portions 14 are formed, the mask layer 12is removed by hydrofluoric acid or the like. Such a state is shown inFIG. 1C.

[0061] As shown in FIG. 1D, GaN doped with Si is grown on the surface,having the difference-in-height portions 14, of the GaN layer 11 byepitaxial growth, to form a crystal growth layer 15 including facetstructures 17 each having inclined planes. The epitaxial growth may beperformed, after the substrate temperature is raised, in accordance witha vapor phase epitaxial (VPE) process, an organic metal chemical vapordeposition (MOCVD), or the like. At the time of crystal growth, thereappears a facet structure having inclined planes with elapsed time dueto a difference in crystal growth rate between different planes of eachdifference-in-height portion 14. Such an inclined plane is designated byreference numeral 16 in FIG. 1D, which may be typically an S-plane, thatis, the {1-101} plane, or {11-22} plane. Depending on the shape of thestripe shaped difference-in-height portion 14, a pair of the inclinedplanes 16 are opposed to each other at the low-level portion, that is,the valley of the difference-in-height portion 14. That is to say, eachfacet structure, designated by reference numeral 17, is configured as aprojecting rib which is formed into an approximately inverse-V shape incross-section and which extends along the longitudinal direction of thestripe shape of the difference-in-height portion 14.

[0062] As shown in FIG. 1E, after the crystal growth layer 15 includingthe facet structures 17 each having the inclined planes 16 is formed, aGaN layer doped with Si is formed on the crystal growth layer 15, anInGaN layer is formed thereon under a condition that the growthtemperature is lowered, and a GaN layer 18 doped with Mg is formedthereon. The GaN layer doped with Si functions as a first conductivecladding layer, the InGaN layer functions as an active layer, and theGaN layer 18 doped with Mg functions as a second conductive claddinglayer. It is to be noted that the GaN layer doped with Si and the InGaNlayer, which are formed under the GaN layer 18 doped with Mg, aredepicted by a line 19. These layers forming a light emission region,which are formed on the facet structures 17 each having the inclinedplanes 16, extend in parallel to the inclined planes 16. A thickness ofthe InGaN layer may be in a range of about 0.5 nm to about 10 mn,preferably, about 1 nm to about 3 mn. The InGaN layer may be replacedwith a quantum well structure having an (Al)GaN/InGaN structure, amulti-quantum well structure, a multi-structure using a GaN layer or anInGaN layer as a guide layer or other suitable structure. At this time,an AlGaN layer may be grown on the InGaN layer. In this regard, sincethe active layer and the cladding layers are directly formed on thefacet structures 17 each having the inclined planes 16, it is possibleto eliminate the need of provision of a step of burying the facetstructures each having the inclined planes with the GaN layer. Also inthe case of using the S-planes as the inclined planes, since the numberof bonds of gallium to nitrogen at the S-plane becomes larger than thatat any other crystal plane, it is possible to enhance the quality ofcrystal.

[0063] As shown in FIG. 1F, part of the stacked layers are removed, toform an opening portion 20 reaching the GaN layer 11. A Ti/Al/Pt/Auelectrode is formed by vapor deposition on a portion, exposed within theopening portion 20, of the GaN layer 11. The Ti/Al/Pt/Au electrode istaken as an n-side electrode 21 as shown in FIG. 1F.

[0064] After the n-side electrode 21 is formed, an Ni/Pt/Au electrode orNi(Pd)/Pt/Au electrode is formed by vapor deposition on the uppermostone of the stacked layers, that is, the GaN layer 18 doped with Mg. TheNi/Pt/Au electrode or Ni(Pd)/Pt/Au electrode is taken as a p-sideelectrode 22 as shown in FIG. 1G. In addition, if a transparentelectrode is formed as the p-side electrode, light can be emerged froman upper surface side of the device, and if the thickness of the p-sideelectrode is large, light can be emerged from a lower surface side ofthe device.

[0065] The semiconductor light emitting device thus fabricated has astructure shown in FIG. 1G. As described above, the GaN layer 11 dopedwith silicon is formed on the sapphire substrate 10 with the C+ plane ofsapphire taken as the substrate principal plane; the facet structures 17each having the inclined planes 16 which are inclined with respect tothe C+ plane by making use of the difference-in-height portions 14formed in the surface of the GaN layer 11; and the GaN layer doped withSi, the InGaN layer, and the GaN layer 18 doped with Mg are formed insuch a manner as to extend on the planes parallel to the inclined planes16. In this structure, the InGaN layer held between the two GaN layersis taken as the active layer for emitting light. When a current issupplied to the active layer between the p-side electrode 22 connectedto the GaN layer 18 doped with Mg and the n-side electrode 21 connectedto the GaN layer 11 doped with Si, there occurs light emission of thesemiconductor light emitting device having the above structure.

[0066] In the semiconductor light emitting device having the abovestructure, the facet structures 17 each having the inclined planes 16are formed before the active layer is formed, and consequently, even ifthrough-dislocations are propagated from the substrate, the propagationof the through-dislocations is deflected by the inclined planes 16, witha result that it is possible to suppress occurrence of crystal defects.In this regard, since it is not required to bury the facet structures 17each having the inclined planes 16 with the GaN layer, it is possible toreduce the number of steps and to relatively shorten a time required forfabricating the light emitting device. Further, since the claddinglayers and the active layer are formed by making use of the inclinedplanes 16 which are inclined or diagonally oriented with respect to thesubstrate principal plane, it is possible to form a light emissionregion with good crystallinity because the number of bonds of gallium tonitrogen becomes larger at each inclined plane 16.

[0067] It should be appreciated that the semiconductor devices of thepresent invention can be applied in a variety of different and suitableapplications. For example, the semiconductor light emitting device canbe used not only as a light emitting diode but also as a semiconductorlaser by forming a resonance end face at an end portion of the device,and further, it can be used as a light emitting diode or semiconductorlaser of multi-colors by forming electrodes in two or more lightemission regions different from each other in terms of emissionwavelength as will be described.

Example Two

[0068] In Example Two, a semiconductor light emitting device isfabricated in the same manner as that for fabricating the semiconductorlight emitting device Example One except for formation of a facetstructure.

[0069] As shown in FIG. 2A, a GaN layer 31 doped with silicon is formedat about 1000° C. on a principal plane (C+ plane) of a sapphiresubstrate 30. In addition, a low temperature buffer layer (not shown)made from AlN or GaN can be formed at a low temperature of about 500° C.between the sapphire substrate 10 and the GaN layer 31. It is to benoted that, in the fabrication process according to an embodiment,growth of respective layers are grown substantially at about normal orstandard pressures, for example, about 740 Torr.

[0070] As shown in FIG. 2B, a mask layer 32 made from SiO2 or SiN isformed overall on the GaN layer 31 doped with silicon to a thickness ofabout 100 nm to about 500 nm. The mask layer 12 is patterned, byphotolithography and etching using a photoresist layer, into a patternhaving stripe shaped opening portions 33 spaced parallel from each otherwith a specific pitch. The depth of each opening portion 13 is set suchthat the opening portion 33 reaches the surface of the GaN layer 31. Forexample, each stripe shaped opening portion 33 extends in the <11-20> or<1-100> direction, and a width of the opening portion 33 is in a rangeof about 0.1 μm to about 10 μm. After the opening portions 33 are formedin the mask layer 32, similar to Example One, the resist layer isremoved. In this state, the GaN layer 31 is exposed within the openingportions 33 formed in the mask layer 32.

[0071] A surface of the GaN layer 31 is selectively etched by using themask layer 32 as a mask, so that the surface of the GaN layer 31 isselectively cut off in a pattern depending on the pattern of the stripeshaped opening portions 33, to form stripe shaped difference-in-heightportions 34. The difference-in-height portion 34 has a high-levelportion located directly under a mask portion of the mask layer 32, anda low-level portion located under the opening portion 33. After thedifference-in-height portions 34 are formed, the mask layer 32 isremoved by hydrofluoric acid or the like. Such a state is shown in FIG.2C.

[0072] As shown in FIG. 2D, a crystal growth layer including facetstructures each having inclined planes is formed by epitaxial growth onthe surface, having the difference-in-height portions 34, of the GaNlayer 31. The epitaxial growth may be performed, after the substratetemperature is raised, in accordance with a vapor phase epitaxial (VPE)process, an organic metal chemical vapor deposition (MOCVD), or thelike. During crystal growth, there appears a facet structure 38 havinginclined planes 35 with elapsed time due to a difference in crystalgrowth rate between different planes of each difference-in-heightportion 34. The inclined plane 35 may be typically the {11-22} plane orthe S-plane. Depending on the shape of the stripe shapeddifference-in-height portion 34, a pair of the inclined planes 35 areopposed to each other at the low-level portion, that is, the valley ofthe difference-in-height portion 34. In accordance with this embodiment,a facet bottom surface portion 37 composed of the flat C-plane is formedbetween the pair of inclined planes 35, and a facet top surface portion36 is formed by crystal growth on the high-level portion, kept at theC-plane, of the difference-in-height portion 34.

[0073] As shown in FIG. 2E, after the crystal growth layer including thefacet structures 38 each having the inclined planes 35, the facet bottomsurface portion 37, and the facet top surface portion 36 is formed, aGaN layer doped with Si is formed on the crystal growth layer, an InGaNlayer is formed thereon under a condition that the growth temperature islowered, and a GaN layer 39 doped with Mg is formed thereon. The GaNlayer doped with Si functions as a first conductive cladding layer, theInGaN layer functions as an active layer, and the GaN layer 39 dopedwith Mg functions as a second conductive cladding layer. It is to benoted that the GaN layer doped with Si and the InGaN layer, which areformed under the GaN layer 39 doped with Mg, are depicted by a line 40in FIG. 2E. These layers forming a light emission region, which areformed on the facet structures 38 each having the inclined planes 35,extend in parallel to the inclined planes 35 and also extend in parallelto the facet bottom surface portion 37 having the C-plane and the facettop surface portion 36 having the C-plane. A thickness of the InGaNlayer may be in a range of about 0.5 nm to about 6 nm. The InGaN layermay be replaced with a quantum well structure having an (Al)GaN/InGaNstructure, a multi-quantum well structure, a multi-structure using a GaNlayer or an InGaN layer as a guide layer, or other like structure. Atthis time, an AlGaN layer may be grown on the InGaN layer. In thisregard, since the active layer and the cladding layers are directlyformed on the facet structures 38 each having the inclined planes 35, itis possible to eliminate the need of provision of a step of burying thefacet structures each having the inclined planes with the GaN layer.

[0074] As shown in FIG. 2F, like Example One, part of the stacked layersare removed, to form an opening portion 42 reaching the GaN layer 31. ATi/Al/Pt/Au electrode is formed by vapor deposition on a portion,exposed within the opening portion 42, of the GaN layer 31. TheTi/Al/Pt/Au electrode is taken as an n-side electrode 41 as shown inFIG. 2F.

[0075] After the n-side electrode 41 is formed, like Example One, anNi/Pt/Au electrode or Ni(Pd)/Pt/Au electrode is formed by vapordeposition on the uppermost one of the stacked layers, that is, the GaNlayer 39 doped with Mg. The Ni/Pt/Au electrode or Ni(Pd)/Pt/Au electrodeis taken as a p-side electrode 43 as shown in FIG. 2G.

[0076] The semiconductor light emitting device thus fabricated has astructure shown in FIG. 2G. As described above, the GaN layer 31 dopedwith silicon is formed on the sapphire substrate 30 with the C+ plane ofsapphire taken as the substrate principal plane; the facet structures 38each having the inclined planes 35 which are inclined with respect tothe C+ plane by making use of the difference-in-height portions 34formed in the surface of the GaN layer 31; and the GaN layer doped withSi, the InGaN layer, and the GaN layer 39 doped with Mg are formed insuch a manner as to extend on the planes parallel to the inclined planes35 and on the planes parallel to the C-plane. In this structure, theInGaN layer held between the two GaN layers is taken as the active layerfor emitting light. When a current is supplied to the active layerbetween the p-side electrode 43 connected to the GaN layer 39 doped withMg and the n-side electrode 41 connected to the GaN layer 31 doped withSi, there occurs light emission of the semiconductor light emittingdevice having the above structure.

[0077] In the semiconductor light emitting device having the abovestructure, the facet structures 38 each having the inclined planes 35are formed before the active layer is formed, and consequently, even ifthrough-dislocations are propagated from the substrate, the propagationof the through-dislocations is deflected by the inclined planes 35, witha result that it is possible to suppress occurrence of crystal defects.In this embodiment, since it is not required to bury the facetstructures 38 each having the inclined planes 35 with the GaN layer, itis possible to reduce the number of steps and to decrease a timerequired for fabricating the light emitting device; and since thecladding layers and the active layer are formed by making use of theinclined planes 35 which are inclined with respect to the substrateprincipal plane, it is possible to form a light emission region withgood crystallinity because the number of bonds of gallium to nitrogenbecomes larger at each inclined plane 35.

[0078] As previously discussed, the semiconductor device of the presentinvention can be applied in a variety of suitable applications.

Example Three

[0079] A semiconductor light emitting device in accordance with anembodiment of the present invention can be fabricated by making use of acrystal growth layer which is formed in a pattern of inverse-hexagonalpyramid shapes overall on a substrate principal plane. As shown in FIG.3, a perspective view of a crystal growth layer used for fabricating thesemiconductor light emitting device of an embodiment of the presentinvention is provided. Like the first and second examples, the crystalgrowth layer is obtained by forming a GaN layer 51 doped with silicon ona sapphire substrate 50, forming difference-in-height portions (notshown) in the GaN layer 51 doped with silicon, and growing a GaN layer53 doped with silicon in a pattern of inverse-hexagonal pyramid shapesas shown in FIG. 3.

[0080] As shown in FIG. 4A, a plurality of equilateral hexagonal shapedrecesses 61 are formed in a flat surface of the GaN layer 51 in such amanner that the opposed sides of the adjacent two of the recesses 61 areseparated from each other with a specific gap put therebetween like ahoneycomb pattern or are in contact with each other. To grow aninverse-hexagonal pyramid shaped crystal 63 shown in FIG. 4B, an endportion 62 of the equilateral hexagonal recess, that is, thedifference-in-height portion 61 may extend, for example, in thedirection perpendicular to the <1-100> direction or the <11-20>direction. An angle of the lowest portion of the inverse-hexagonalpyramid shape 63 can be set to about 60° by adjusting a crystal growthcondition. In this case, the crystal layer can be grown in a pattern ofinverse-equilateral hexagonal pyramid shapes. In addition, the crystallayer can be also grown in a pattern of truncated inverse-hexagonalpyramid shapes each having a bottom plane taken as the C-plane.

[0081] After the GaN layer 53 doped with silicon is formed in a patternof inverse-hexagonal pyramid shapes shown in FIG. 3, a GaN layer dopedwith Si, an InGaN layer, a GaN layer doped with Mg are sequentiallystacked on the GaN layer 53. Since each inverse-hexagonal pyramid of thepattern of the GaN layer 53 has inclined planes for forming a facetstructure, the layers stacked thereon extend in parallel to the inclinedplanes. The InGaN layer held between the two GaN layers acts as anactive layer for light emission. It is to be noted that, in thefabrication process according to an embodiment, respective layers aregrown at about normal or standard pressure, for example, about 740 Torr.

[0082] As previously discussed, the semiconduction device of the presentinvention can be applied in a variety of different and suitableapplications.

Example Four

[0083] In an embodiment, an approximately V-shaped light emission regionis formed by using a stripe shaped difference-in-height portion, and anelectrode is formed in the light emission region. The processing stepswill be described with reference to FIGS. 5A to 5F.

[0084] A GaN layer 71 doped with silicon is formed on a principal plane(C+ plane) of a sapphire substrate 70. A low temperature buffer layermay be formed before the GaN layer 71 doped with silicon is formed. LikeExample Two, stripe shaped difference-in height portions are formed in asurface of the GaN layer 71 doped with silicon, followed by continuationof crystal growth by using the difference-in-height portions, to obtainthe GaN layer 71 having approximately V-shaped valleys 72 as shown inFIG. 5A. The approximately V-shaped valley 72 is formed by inclinedplanes opposed to each other at a specific angle. The inclined plane isselected from the S-plane, the {11-22} plane, and planes beingsubstantially equivalent thereto. Although a bottom of the valley 72 isV-shaped at a specific angle as shown, a plane parallel to the C-planemay appear on the bottom of the valley 72.

[0085] A GaN layer doped with Si, an InGaN layer 75 shown by a line inthe figure, and a GaN layer 73 doped with Mg are sequentially stacked onthe GaN layer 71. The GaN layer doped with Si, the InGaN layer 75, andthe GaN layer 73 doped with Mg form a light emission region. Even ateach approximately V-shaped valley 72, the light emission region isformed by the stacked structure of the GaN layer doped with Si, theInGaN layer 75, and the GaN layer 73 doped with Mg. Subsequently, asilicon oxide layer 74 is formed overall on the stacked structure insuch a manner as to cover the inside of each approximately V-shapedvalley 72. It is to be noted that in the fabrication process, respectivelayers are grown at about normal or standard pressure, for example,about 740 Torr.

[0086] After formation of the silicon oxide layer 74 overall on thestacked structure, a resist layer 76 is formed overall on the siliconoxide layer 74. As shown in FIG. 5B, an opening portion 77 is formed, bya photolithography technique, in the resist layer 76 at a positioncorresponding to the approximately V-shaped valley 72 in which anelectrode is to be formed. The depth of the opening portion 77 reachesthe surface of the silicon oxide layer 74. In addition, the width of theopening portion 72 is shorter than a width of an opening of theapproximately V-shaped valley 72, so that only the inclined planes ofthe valley 72 are exposed within the opening portion 77.

[0087] A portion of the silicon oxide layer 74, located at the positioncorresponding to the approximately V-shaped valley 72, is removed by RIE(Reactive Ion Etching) or wet etching using a hydrofluoric acid basedetchant via the opening portion 77 of the resist layer 76. With thepartial removal of the silicon oxide layer 74 at the valley 72, the GaNlayer 73 doped with Mg is exposed at the valley 72. The resist layer 76is then removed and a resist layer 78 for forming an electrode by aliftoff process is formed. The resist layer 78 has a window portion 79at a position at which the surface of the GaN layer 73 is exposed. Morespecifically, as shown in FIG. 5C, a cross-sectional portion of thesilicon oxide layer 74 and the GaN layer 73 doped with Mg are exposedwithin the window portion 79 of the resist layer 78.

[0088] After the mask of the resist layer 78 and the silicon oxide layer74 is formed, as shown in FIG. 5D, a p-side electrode material such asNi/Pt/Au or Ni(Pd)/Pt/Au is deposited via the window portion 79, to forma p-side electrode material layer 80. Since a height differenceequivalent to the total height of the resist layer 78 and the siliconoxide layer 74 lies between the top and the bottom of the window portion79, the film is thinned or not formed at the stepped portion of thewindow portion 79, whereby a p-side electrode 81 being approximatelyV-shaped in cross section is formed at the valley 72.

[0089] After the p-side electrode 81 is formed at the valley 72, asshown in FIG. 5E, the resist layer 78 on the silicon oxide layer 74 isremoved (that is, lifted off) by using a solvent such as acetone, toremove the p-side electrode material layer 80 excluding the p-sideelectrode 81 at the valley 72. Finally, an opening portion 82 is formedin such a manner as to reach the GaN layer 71 doped with Si, and ann-side electrode 83 is formed as shown in FIG. 5F.

[0090] In accordance with the above-described fabrication steps, evenwhen an approximately V-shaped light emission region is formed by usinga stripe shaped difference-in-height portion, the p-side electrode 81being approximately V-shaped in cross-section can be formed at thevalley 72 in the light emission region, to allow injection of a currentin the light emission region.

Example Five

[0091] In an embodiment, the semiconductor device of the presentinvention can include substantially V-shaped valleys that are formed byusing stripe shaped difference-in-height portions, a light emissionregion that is formed in a flat portion, parallel to the C-plane,located between the valleys, and an electrode that is formed in thelight emission region. The processing steps of this example will bedescribed with reference to FIGS. 6A to 6D.

[0092] A GaN layer 91 doped with silicon is formed on a principal plane(C+ plane) of a sapphire substrate 90. A low temperature buffer layermay be formed before the GaN layer 91 doped with silicon is formed. Likethe second embodiment, stripe shaped difference-in height portions areformed in a surface of the GaN layer 91 doped with silicon, followed bycontinuation of crystal growth by using the difference-in-heightportions, to obtain the GaN layer 91 having approximately V-shapedvalleys 92 as shown in FIG. 6A. The approximately V-shaped valley 92 isformed by inclined planes opposed to each other at a specific angle. Theinclined plane is selected from the S-plane, the {11-22} plane, andplanes being substantially equivalent thereto. Although a bottom of thevalley 92 is V-shaped at a specific angle in this embodiment, a planeparallel to the C-plane may appear on the bottom of the valley 92.

[0093] A GaN layer doped with Si, an InGaN layer shown by a line in thefigure, and a GaN layer 93 doped with Mg are sequentially stacked on theGaN layer 91. The GaN layer doped with Si, the InGaN layer, and the GaNlayer 93 doped with Mg form a light emission region. Even at eachapproximately V-shaped valley 92, the light emission region is formed bythe stacked structure of these GaN layer doped with Si, the InGaN layer,and the GaN layer 93 doped with Mg. Subsequently, a silicon oxide layer94 is formed overall on the stacked structure in such a manner as tocover the inside of each approximately V-shaped valley 92. It is to benoted that in the fabrication process, respective layers are grown atabout normal pressure, for example, about 740 Torr.

[0094] After formation of the silicon oxide layer 94 overall on thestacked structure, as shown in FIG. 6B, a resist layer is formed overallon the silicon oxide layer 94 and an opening portion is formed, by thephotolithography technique, in the resist layer at a positioncorresponding to a flat portion, parallel to the C-plane, in which anelectrode is to formed. A portion of the silicon oxide layer 94, locatedat the opening portion, is removed by RIE or wet etching using, forexample, a hydrofluoric acid-based etchant, to form a window portion 95having a shape corresponding to that of the opening portion in thesilicon oxide layer 94. The depth of the window portion 95 reaches thesurface of the silicon oxide layer 93 doped with Mg.

[0095] After formation of the window portion 95, a resist layer 96 forforming a p-side electrode, which has a window portion 96 d, is formedby photolithography. The window portion 96 d is slightly wider than thewindow portion 95, so that part of the silicon oxide layer 94 and thesurface of the GaN layer 93 doped with Mg are exposed within the windowportion 96 d.

[0096] After the mask of the resist layer 96 and the silicon oxide layer94 is formed, as shown in FIG. 6C, a p-side electrode material such asNi/Pt/Au or Ni(Pd)/Pt/Au is deposited via the window portion 96 d, toform a p-side electrode material layer 97. Since a height differenceequivalent to the total height of the resist layer 96 and the siliconoxide layer 94 lies between the top and the bottom of the window portion96 d, the film is thinned or not formed at the stepped portion of thewindow portion 96 d, whereby a p-side electrode 98 having a plug-likeshape with flanges on the upper side in cross section is formed in thewindow portion 95.

[0097] After the p-side electrode 98 is formed, as shown in FIG. 6D, theresist layer 96 on the silicon oxide layer 94 is removed by using asolvent such as acetone, to remove the p-side electrode material layer97 excluding the p-side electrode 98. Finally, an opening portion 100 isformed in such a manner as to reach the GaN layer 91 doped with Si, andan n-side electrode 99 is formed.

[0098] According to the above-described fabrication steps, even whenapproximately V-shaped valleys are formed by using stripe shapeddifference-in-height portions and a light emission region is formed in aflat portion, parallel to the C-plane, located between the valleys, theplug-like p-side electrode 98 can be formed on the flat portion in thelight emission region, to allow injection of a current in the lightemission region.

Example Six

[0099] As shown in FIG. 7, a multi-color light emitting device isfabricated, wherein two independent electrodes are provided to form along-wavelength light emission region and a short-wavelength lightemission region in accordance with an embodiment of the presentinvention.

[0100] A GaN layer 111 doped with silicon is formed on a principal plane(C+ plane) of a sapphire substrate 110, and different-in-height portionsare formed in a surface of the GaN layer 111. Subsequently, facetstructures each having inclined planes 112 inclined with respect to thesubstrate principal plane are formed by making use of thedifference-in-height portions. It is to be noted that in the fabricationprocess, respective layers are formed at about normal pressure, forexample, about 740 Torr. A stacked structure of a GaN layer doped withSi, an InGaN layer, and a GaN layer 115 doped with Mg is formed so as toextend on a plane parallel to the inclined planes 112 and the C-plane.The InGaN layer held between the two GaN layers acts as an active layerfor emitting light.

[0101] As shown in FIG. 7, an n-side electrode 116 is connected to theGaN layer 111 doped with Si; and a p-side electrode is composed a p-sideelectrode 113 for a long-wavelength light emission region, which ispositioned at an approximately V-shaped valley formed by the inclinedplanes 112, and a p-side electrode 114 for a short-wavelength lightemission region, which is formed on a flat portion 117 between theadjacent approximately V-shaped valleys. An active layer formed at theapproximately V-shaped valley has a structure determined on the basis ofa composition and a thickness of the active layer, which structureallows emission of light having a long-wavelength, for example, emissionof light of green or red. In this regard, by injecting a current in theactive layer via the p-side electrode 113, it is possible to realizeemission of light having a long-wavelength, for example, emission oflight of green or red. An active layer formed on the flat portion 117between the adjacent approximately V-shaped valleys has a structuredetermined on the basis of a composition and a thickness of the activelayer, which structure allows emission of light having ashort-wavelength, for example, emission of light of blue. In thisregard, by injecting a current in the active layer via the p-sideelectrode 114, it is possible to realize emission of light having ashort-wavelength, for example, emission of light of blue.

[0102] Even if through-dislocations are propagated from the substrate,the propagation of the through-dislocations is deflected by the inclinedplanes 112, to suppress occurrence of crystal defects, and since thefacet structures are not buried with the GaN layer, it is possible tofabricate the device for a relatively short time without increasing thenumber of processing steps. Further, light emission regions for emittinglight having different wavelengths can be formed on the same device bymaking use of a difference in composition and thickness between one ormore of the active layers formed on respective crystal planes of thefacet structure. In this regard, since the p-side electrodes 113 and 114are disposed on the upper and lower sides of the difference-in-heightportion, it is possible to form electrodes in micro-sized light emissionregions without occurrence of any problem of short-circuit.

Example Seven

[0103] As shown in FIG. 8, a multi-color light emitting device inaccordance with an embodiment of the present invention is provided, isfabricated, wherein three independent electrodes are provided to form ared light emission region, a green light emission region, and a bluelight emission region.

[0104] A GaN layer 121 doped with silicon is formed on a principal plane(C+ plane) of a sapphire substrate 120, and different-in-height portionsare formed in a surface of the GaN layer 121. Subsequently, facetstructures each having inclined planes 122 inclined with respect to thesubstrate principal plane are formed by making use of thedifference-in-height portions. It is to be noted that in the fabricationprocess, respective layers are formed at about normal pressure, forexample, about 740 Torr. A stacked structure of a GaN layer doped withSi, an InGaN layer, and a GaN layer 125 doped with Mg is formed so as toextend on a plane parallel to the inclined planes 122 and the C-plane.The InGaN layer held between the two GaN layers acts as an active layerfor emitting light.

[0105] In an embodiment, to the semiconductor light emitting device ofthe present invention includes an n-side electrode 126 is connected tothe GaN layer 121 doped with Si; and a p-side electrode is composed ap-side electrode 123 for a red light emission region, which ispositioned at an approximately V-shaped valley formed by the inclinedplanes 122, a p-side electrode 124 for a blue light emission region,which is formed on an upper flat portion 128 between the adjacentapproximately V-shaped valleys, and a p-side electrode 127 for a greenlight emission region, which is formed on a lower flat portion 129. Anactive layer formed at the approximately V-shaped valley has a structuredetermined on the basis of a composition and a thickness of the activelayer, which structure allows emission of light of red. In this regard,by injecting a current in the active layer via the p-side electrode 123,it is possible to realize emission of light of red. An active layerformed on the upper flat portion 128 between the adjacent approximatelyV-shaped valleys has a structure determined on the basis of acomposition and a thickness of the active layer, which structure allowsemission of light of blue. In this regard, by injecting a current in theactive layer via the p-side electrode 124, it is possible to realizeemission of light of blue. An active layer formed on the lower flatportion 129 has a structure determined on the basis of a composition anda thickness of the active layer, which structure allows emission oflight of green, and accordingly, by injecting a current in the activelayer via the p-side electrode 127, it is possible to realize emissionof light of green.

[0106] Even if through-dislocations are propagated from the substrate,the propagation of the through-dislocations is deflected by the inclinedplanes 122, to suppress occurrence of crystal defects, and since thefacet structures are not buried with the GaN layer, it is possible tofabricate the device for a relatively short time without increasing thenumber of processing steps. Further, light emission regions for emittinglight having different wavelengths, particularly, light of red, blue,and green can be formed on the same device by making use of a differencein composition and thickness between one or more of the active layersformed on respective crystal planes of the facet structure. In thisregard, since the p-side electrodes 123, 124, and 127 are disposed atthree different points of the difference-in-height portion, that is,spatially separated from each other, it is possible to form electrodesin micro-sized light emission regions without occurrence of any problemof short-circuit.

[0107]FIG. 9 illustrates a state in which light is emitted from thesemiconductor light emitting device according to an embodiment of thepresent invention such that the semiconductor light emitting device canbe used, for example, as a light emitting diode. In this case, light 130is emerged from the back side of the device. The light 130 may be lightof a single color, multi-colors, or a mixture of colors. The colors oflight 130 can be controlled by applying currents to the p-sideelectrodes 123, 124, and 127. It should be appreciated that thesemiconductor light emitting device of the present invention can be in avariety of other suitable applications, including a semiconductor laserby forming a resonator end face at an end portion of the device. In theexample shown in FIG. 9, red laser light 133R, blue laser light 133B,and green laser light 133G are emerged from the end face of theresonator of the device. The end face of the resonator may be formed bycleavage.

Example Eight

[0108] According to an embodiment of the present invention, asemiconductor light emitting device capable of emitting white light canbe fabricated, wherein as shown in FIG. 10, three independent electrodesare formed, and a common electrode for commonly driving the threeelectrodes is provided.

[0109] A GaN layer 141 doped with silicon is formed on a principal plane(C+ plane) of a sapphire substrate 140, and different-in-height portionsare formed in a surface of the GaN layer 141. Subsequently, facetstructures each having inclined planes 143 inclined with respect to thesubstrate principal plane are formed by making use of thedifference-in-height portions. These fabrication steps are the same asthose described in the previous embodiments. A stacked structure of aGaN layer doped with Si, an InGaN layer, and a GaN layer 142 doped withMg is formed so as to extend on a plane parallel to the inclined planes143 and the C-plane. The InGaN layer held between the two GaN layersacts as an active layer for emitting light.

[0110] According to an embodiment, the semiconductor of the presentinvention can include an n-side electrode 148 that is connected to theGaN layer 141 doped with Si via an opening portion; and a p-sideelectrode is, like Example Seven, composed a p-side electrode 144 for ared light emission region, which is positioned at an approximatelyV-shaped valley formed by the inclined planes 143, a p-side electrode145 for a blue light emission region, which is formed on an upper flatportion between the adjacent approximately V-shaped valleys, and ap-side electrode 146 for a green light emission region, which is formedon a lower flat portion. In an embodiment, a common electrode 147 forcommonly driving the p-side electrodes 144, 145 and 146 is formed. Withthe acid of this common electrode 147, the device fabricated as themulti-color light emitting device can be used as a light emitting devicecapable of emitting white light.

[0111] Even if through-dislocations are propagated from the substrate,the propagation of the through-dislocations is deflected by the inclinedplanes 143, to suppress occurrence of crystal defects, and since thefacet structures are not buried with the GaN layer, it is possible tofabricate the device for a relatively short time without increasing thenumber of processing steps. Further, according to an embodiment, sincelight emission regions for emitting light of red, blue, and green can beformed on the same device by making use of a difference in compositionand thickness between one or more of the active layers formed onrespective crystal planes of the facet structure, it is possible to emitwhite light by commonly driving the electrodes formed in the lightemission regions. The semiconductor light emitting device of the presentinvention, therefore, can be used as an illuminating unit or applied ina variety of other suitable applications.

Example Nine

[0112] In an embodiment of the present invention, a semiconductor lightemitting device capable of emitting white light is fabricated, whereinas shown in FIG. 11, three independent electrodes are formed, and acommon electrode for commonly driving the three electrodes is provided.

[0113] A GaN layer 141 doped with silicon is formed on a principal plane(C+ plane) of a sapphire substrate 140, and different-in-height portionsare formed in a surface of the GaN layer 141. Subsequently, facetstructures each having inclined planes 143 inclined with respect to thesubstrate principal plane are formed by making use of thedifference-in-height portions. These fabrication steps are the same asthose described in the previous embodiments. A stacked structure of aGaN layer doped with Si, an InGaN layer, and a GaN layer 142 doped withMg is formed so as to extend on a plane parallel to the inclined planes143 and the C-plane. The InGaN layer held between the two GaN layersacts as an active layer for emitting light.

[0114] In an embodiment, the semiconductor device of the presentinvention includes an n-side electrode 148 is connected to the GaN layer141 doped with Si via an opening portion; and a p-side electrode is,like Example Seven, composed of a p-side electrode 144 for a red lightemission region, which is positioned at an approximately V-shaped valleyformed by the inclined planes 143, a p-side electrode 145 for a bluelight emission region, which is formed on an upper flat portion betweenthe adjacent approximately V-shaped valleys, and a p-side electrode 146a for a green light emission region, which is formed on the inclinedplane 143. In an embodiment, a common electrode 147 for commonly drivingthe p-side electrodes 144, 145 and 146 a is formed. With the acid ofthis common electrode 147, the device fabricated as the multi-colorlight emitting device can be used as a light emitting device capable ofemitting white light.

[0115] Even if through-dislocations are propagated from the substrate,the propagation of the through-dislocations is deflected by the inclinedplanes 143, to suppress occurrence of crystal defects, and since thefacet structures are not buried with the GaN layer, it is possible tofabricate the device for a relatively short time without increasing thenumber of processing steps. Further, since light emission regions foremitting light of red, blue, and green can be formed on the same deviceby making use of a difference in composition and thickness between oneand another of the active layers formed on respective crystal planes ofthe facet structure, it is possible to emit white light by commonlydriving the electrodes formed in the light emission regions. Thesemiconductor light emitting according to an embodiment, therefore, canbe used as an illuminating unit or applied in other suitableapplications.

Example Ten

[0116] In an embodiment, a semiconductor light emitting device of thepresent invention includes a structure shown in FIG. 12 as fabricated. AGaN layer 151 doped with silicon is formed on a principal plane (C+plane) of a sapphire substrate 150, and different-in-height portions 154are formed in a surface of the GaN layer 15 1. Subsequently, facetstructures each having inclined planes inclined with respect to thesubstrate principal plane are formed by making use of thedifference-in-height portions 154. A stacked structure of a GaN layer159 doped with Si (shown by a line in the figure), an InGaN layer 160,and a GaN layer 158 doped with Mg (shown by a line in the figure) isformed so as to extend on a plane parallel to the inclined planes. TheInGaN layer 160 held between the two GaN layers acts as an active layerfor emitting light. An n-side electrode 161 is connected to the GaNlayer 151 doped with Si, and a p-side electrode 162 is connected to theGaN layer 158 doped with Mg. The device emits light by supplying acurrent to the active layer between the p-side electrode 162 and then-side electrode 161.

[0117] A current quantity adjusting circuit 170 is connected between thep-side electrode 162 and the n-side electrode 161 for adjusting acurrent quantity so as to set an emission wavelength of thesemiconductor light emitting device to a desired wavelength. Forexample, the current quantity adjusting circuit 170 can output a signalhaving a waveform (a) of cyclic pulses each having a short pulse widthand a high peak value and a waveform (b) of cyclic pulses each having arelatively long pulse width and a low peak value. When a signal havingthe waveforn (a) is supplied between the p-side electrode 162 and then-side electrode 161 from the current quantity adjusting circuit 170,light of a short-wavelength can be emitted from the device, and when asignal having the waveform (b) is supplied between the p-side electrode162 and the n-side electrode 161 from the current quantity adjustingcircuit 170, light of a long-wavelength can be emitted from the device.In this way, the emission wavelength can be set to a desired wavelengthby controlling a quantity of a current supplied to the device and awaveform of a signal supplied to the device.

[0118] As described above, the semiconductor light emitting device andthe method of fabricating the semiconductor light emitting deviceaccording to an embodiment of the present invention, even ifthrough-dislocations are propagated from the substrate, the propagationof the through-dislocations is deflected by the inclined planes, tosuppress occurrence of crystal defects. Further, since the facetstructures are not buried with the GaN layer, it is possible tofabricate the device for a relatively short time without increasing thenumber of processing steps.

[0119] Since cladding layers and an active layer are formed on a planeextending in parallel to an inclined plane inclined with respect to thesubstrate principal plane, a portion having a good crystallinity can beused as a light emission region by making use of the increased number ofbonds of gallium to nitrogen at the inclined plane.

[0120] With the multi-color semiconductor light emitting device and themethod of fabricating the multi-color semiconductor light emittingdevice according to an embodiment of the present invention, lightemission regions for emitting light having different wavelengths,particularly, light of red, blue, and green can be formed on the samedevice by making use of a difference in composition and thicknessbetween one or more active layers formed on respective crystal planes ofa facet structure. Since respective electrodes, for example, p-sideelectrodes are disposed at three different points of thedifference-in-height portion, that is, spatially separated from eachother, it is possible to form electrodes in micro-sized light emissionregions without occurrence of any problem of short-circuit.

[0121] It should be understood that various changes and modifications tothe presently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

The invention is claimed as follows:
 1. A semiconductor light emittingdevice comprising: a substrate having a surface that has adifference-in-height portion; a crystal growth layer formed on thesurface of the substrate wherein at least a portion of the crystalgrowth layer is oriented along an inclined plane with respect to thesurface of the substrate; and a first conductive layer, an active layerand a second conductive layer formed on the crystal growth layer in astacked arrangement and oriented along the inclined plane.
 2. The deviceof claim 1 wherein the substrate comprises a wurtzite compound.
 3. Thedevice of claim 1 wherein the wurtzite compound forms a layer orientedalong a principal place of the substrate and wherein the inclined planeis inclined with respect to the principal plane.
 4. The device of claim1 wherein the inclined plane comprises at least one of a S-plane and a{11-22} plane.
 5. The device of claim 1 wherein the difference-in-heightportion comprises a shape selected from the group consisting of a stripeshape, a rectangular shape, a round shape, a triangular shape, ahexagonal shape and combinations thereof.
 6. The device of claim 1wherein the crystal growth layer comprises a shape selected from thegroup consisting of a stripe shape, a rectangular shape, a round shape,a triangular shape, a hexagonal shape and combinations thereof.
 7. Thedevice of claim 1 wherein the crystal growth layer further comprises aportion which is substantially parallel with respect to a principalplane along which at least a portion of the substrate is oriented. 8.The device of claim 1 wherein the semiconductor light emitting devicecomprises a light emitting diode structure.
 9. The device of claim 1wherein the semiconductor light emitting device comprises asemiconductor laser structure.
 10. The device of claim 1 wherein thesurface of the substrate is oriented along a C-plane such that an endportion of the different-in-height portion is oriented perpendicularwith respect to at least one of a <1-100> direction and a <1-20>direction and wherein the growth of the crystal growth layer depends ona shape of the difference-in-height portion.
 11. The device of claim 1wherein at least a portion of the crystal growth layer forms a valleyhaving a cross-section that is substantially V-shaped.
 12. The device ofclaim 11, wherein an electrode is formed on the substantially V-shapedvalley.
 13. A device of claim 1, wherein said crystal growth layer has aplurality of crystal growth layer portions perpendicularly formed withina plane being approximately parallel to a principal plane of thesubstrate.
 14. The device of claim 1, wherein the crystal growth layercomprises a GaN semiconductor.
 15. The device of claim 1, wherein thecrystal growth layer is grown at a temperature of about 1100° C. orless.
 16. The device of claim 1, wherein the crystal growth layer isgrown at pressure of about 100 Torr or more.
 17. A semiconductor lightemitting device comprising: a substrate comprising a substrate layercomposed of a wurtzite compound formed along a principal plane of thesubstrate wherein the layer includes a different-in-height portionformed in a surface of the substrate layer; a crystal growth layerformed on the surface of the substrate layer wherein at least a portionof the crystal growth layer is oriented along an inclined plane that isinclined with respect to the principal plane; a first conductivecladding layer, an active layer and a second conductive layer formed onthe crystal growth layer in a sequentially stacked arrangement orientedalong two or more planes of the crystal growth layer including theinclined plane such that one or more light emission regions are formed;and one or more electrodes separately formed in the light emissionregions.
 18. The device of claim 17, wherein the inclined planecomprises at least one of an S-plane and a {11-22} plane.
 19. The deviceof claim 17, wherein the principal plane comprises at least one of aC-plane and a {0001} plane.
 20. The device of claim 17, whereinwavelengths of two or more kinds of light emitted from the lightemission regions are different from each other.
 21. The device of claim20, wherein at least one of a composition and a thickness of the activelayer varies with respect to the light emission regions such that thewavelengths are different from each other.
 22. The device of claim 17,wherein the light emitting device has a light emitting diode structureallowing simultaneous emission of light associated with two or morecolors.
 23. The device of claim 17, wherein the light emitting devicehas a semiconductor laser structure allowing simultaneous emission oflight of two or more colors.
 24. The device of claim 17, wherein thesubstrate layer is oriented along a C-plane such that an end portion ofthe different-in-height portion is perpendicularly directed with respectto at least one of a <1-100> direction and a <11-20> direction andwherein the growth of the crystal growth layer depends on a shape of thedifferent-in-height portion.
 25. The device of claim 17, wherein atleast a portion of the crystal growth layer forms a valley having across-section that is approximately V-shaped.
 26. The device of claim25, wherein at least one of the electrodes is formed on theapproximately V-shaped valley.
 27. The device of claim 17, wherein thecrystal growth layer comprises a GaN semiconductor.
 28. The device ofclaim 17, wherein the crystal growth layer is grown at a temperature ofabout 1100° C. or less.
 29. The device of claim 17, wherein the crystalgrowth layer is grown at a pressure of about 100 Torr or more.
 30. Amethod of fabricating a semiconductor light emitting device, comprisingthe steps of: forming a wurtzite-type compound semiconductor layer on asubstrate oriented along a principal plane such that adifference-in-height portion is formed in a surface of the wurtzite-typecompound semiconductor; forming a crystal growth layer at least aportion of which is oriented along an inclined plane inclined withrespect to the principal plane by crystal growth on the surface; andapplying a first conductive cladding layer, an active layer, and asecond conductive layer in a stacked arrangement along a regionextending in parallel to said inclined plane.
 31. The method of claim 30comprising the steps subsequent to the applying step of: forming a firstmask material layer, forming a first window region in the first maskmaterial layer, and forming a first electrode layer through the firstwindow region; and forming a second mask material layer, forming asecond window region in the second mask material layer at a positiondifferent from that of the first window region, and forming a secondelectrode layer through the second window region; wherein one or morelight emission regions having different characteristics are formed byusing the first electrode layer and the second electrode layer.
 32. Themethod of claim 30, wherein the semiconductor light emitting device isseparated into a plurality of light emission regions electricallyindependent from each other.
 33. The method claim 32, wherein an amountof current injected in the light emission regions is capable of beingadjusted to establish wavelengths of light emitted from the lightemission regions to a desired value.
 34. The method of claim 30comprising the steps subsequent to the applying step of: forming aresist layer, and forming a specific pattern of an electrode layer by alift-off process.
 35. The method of claim 30 comprising the stepssubsequent to the applying step of: forming a resist layer having awindow region, forming an electrode layer to cover said resist layerincluding an inner region of said window region, and removing saidresist layer together with said electrode layer excluding an electrodeportion formed on a bottom region of the window region by a lift offprocess.
 36. The method of claim 30, wherein the crystal growth layer isgrown at a temperature of about 1100° C. or less.
 37. The method ofclaim 30, wherein the crystal growth layer is grown at a pressure ofabout 100 Torr or more.